Synthesis and conformational analysis of phosphorylated β-(1→2) linked mannosides

Recent advances in chemical synthesis of phosphodiester linkages found in fungal mannans

Fungal mannans are located on the exterior of the fungal cell wall, where they interact with the environment and, ultimately, the human host. Mannans play a major role in shaping the innate immune response to fungal pathogens. Understanding the phosphodiester linkage and mannosyl repeat units in the acid-labile portion of mannans is crucial for comprehending their structure/activity relationships and for development of anti-fungal vaccines and immunomodulators. The phosphodiester linkages connect the acid-stable and acid-labile portions of the mannan polymer. Phosphate groups are attached to positions 4 and/or 6 of mannosyl repeat units in the acid-stable portion and to position 1 of mannosyl repeat units in the acid-labile portion. This review focuses on the synthesis of phosphodiester linkages as an approach to the development of mannan glycomimetics, which are based on natural product fungal mannans. Development of successful synthetic strategies for the phosphodiester linkages may enable the production of mannan glycomimetics that elicit anti-fungal immune responses against existing and emerging fungal pathogens, such as Candida albicans and Candida auris.

Efficient synthesis of α(1,2)-linked oligomannoside derivatives through one-pot glycosylation

An α(1,2)-linked oligomannoside derivative having a free C-2 hydroxyl group and a C-3 pivaloyl group was synthesized from a thiophenyl mannose derivative 1 using a one-pot self-condensation and applying a α-stereoselective procedure. The mannosylation exclusively generated α-mannoside linkages. The observed α-directing effect was rationalized by the remote participation of the pivaloyl group in C-3 position. The polymerization degree was controlled by the promoter amount providing the mannobiose derivative as a major product. Applying this method eliminated many synthetic steps. The α(1,2)-linked oligomannoside derivatives, which are key intermediates for the synthesis of oligomannose type N-glycans for glycoproteins, were easily prepared.

Recent advances in the synthesis of fungal antigenic oligosaccharides

The driving force for the constant improvement and development of new synthetic methodologies in carbohydrate chemistry is a growing demand for biologically important oligosaccharide ligands and neoglycoconjugates thereof for numerous biochemical investigations such as cell-to-pathogen interactions, immune response, cell adhesion, etc. Here we report our syntheses of the spacer-armed antigenic oligosaccharides related to three groups of the polysaccharides of the fungal cell-wall including α- and β-mannan, α- and β-glucan and galactomannan chains, which include new rationally designed synthetic blocks, efficient solutions for the stereoselective construction of glycoside bonds, and novel strategy for preparation of furanoside-containing oligosaccharides based on recently discovered pyranoside-into-furanoside (PIF) rearrangement.

Posttranslational modifications of intact proteins detected by NMR spectroscopy: application to glycosylation

Posttranslational modifications (PTMs) are an integral part of the majority of proteins. The characterization of structure and function of PTMs can be very challenging especially for glycans. Existing methods to analyze PTMs require complicated sample preparations and suffer from missing certain modifications, the inability to identify linkage types and thus chemical structure. We present a direct, robust, and simple NMR spectroscopy method for the detection and identification of PTMs in proteins. No isotope labeling is required, nor does the molecular weight of the studied protein limit the application. The method can directly detect modifications on intact proteins without sophisticated sample preparation. This approach is well suited for diagnostics of proteins derived from native organisms and for the quality control of biotechnologically produced therapeutic proteins.